Electrophoresis is an essential tool for analytical molecular biology, and is increasingly being used for the purification of various kinds of chemical substances. Electrophoretic separations are generally accomplished by establishing an electric field through a conducting medium containing charged particles, with the result that the charged particles are induced to migrate within the electrical field and through the conducting medium.
When the conducting medium is a porous solid or colloidal mixture, the resulting migration of the charged particles through this solid matrix can result in their separation by size, due to the differential migrating rates of variously sized particles through such a medium. Agarose gel electrophoresis is an example of electrophoretic separation in this manner, and is most commonly used to size and separate nucleic acids into discrete bands within the gel for analysis. The gel forms the solid matrix where the separation occurs and is usually generally surrounded by a buffered electrolyte containing solution, or buffer, which evenly conducts the electric field from the electrodes through the gel, and also serves in absorbing and dissipating heat from the operation.
The separation of other biochemical components can be accomplished by this same technique or by any of a wide variety of similar techniques. Proteins or nucleic acids can be separated by size through the use of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Solid matrix gels are also useful in techniques for separation by the charge of the sample particles alone, such as in isoelectric focusing, where the electrical field generates a pH gradient within a gel and the sample particles migrate differentially, dictated by their dissimilar charges, to discrete points along this pH gradient. This is most commonly utilized in separating proteins by their isoelectric points.
In any case, the application of an electrical field consequently results in the generation of Joule heat, the heat resulting from the passage of an electric current through a resistance, and in those applications utilizing electric fields of higher amperages and voltages the amount of such heat can be considerable. This additional heat can have an adverse affect on the efficiency of the electrophoretic separation, and in extreme cases can result in the partial melting of all or portions of the matrix material. Further the substances being electrophoretically separated may be degraded to the point of loss of biochemical activity by the heat so generated. This is a particular problem in those applications where the electrophoretic separation is conducted rapidly by utilizing a more powerful electrical field, or in pulsed field or alternating field electrophoresis techniques. These last techniques generate higher amounts of heat for the same amount of separation achieved, due to the varying and alternating directions of the applied electrical fields. The heat dissipated into the conducting fluid and the electrophoresis medium increases in relation to the amount of applied electrical power.
Thus, if one wishes to use higher electrical power levels to decrease the time for a given electrophoretic separation, or if one is utilizing the pulsed field or alternating field electrophoretic techniques, it is important to address the issue of heat generation within the separation medium or the buffer which is in contact with both the medium and the electrodes. Various apparatus have been proposed for dissipating this heat, such as cooling the buffer by chilling the buffer wells, or in some cases cooling the solid matrix, or gel plate, directly. The primary and most satisfactory method thus far has been to cool the buffer by passing it through tubing immersed in a chilled environment, such as through a bucket of ice water or the like. Heat is exchanged between the liquids across the tubing, and the buffer that is ultimately returned to the electrophoresis chamber has a greatly reduced temperature. Such a method, however, requires a number of different bulky components, which makes the overall operation both cumbersome and requires the utilization of a large amount of bench space. It is also difficult to control the amount of cooling in such a system. Commonly utilized plastic tubing is not known for its heat exchanging ability.